You know that love-hate relationship we have with fatty foods? Well, the same holds true for glycerin, according to Marsha Coulton, founder of Curl Junkie.

“If you use too much, it can be too heavy and feel like an oil in your hair,” Coulton says. “If you use too little, you don’t get the effect you're looking for.”

Just as fats (at least the good ones!) are important in a healthy diet, glycerin is a coveted ingredient when it comes to feeding our curls the moisture they crave. Coulton uses glycerin in both of her curl sprays, but in different proportions. Curl Fuel, which is heavier, has more glycerin. But she cut the glycerin by a third for her Curly Boost spray because too much can weigh down curlies with fine hair.

“I wouldn’t say glycerin is a miracle ingredient because it’s all in the proportions and combinations,” Coulton says, “but it is one of the most useful ingredients.”

You’ll likely see glycerin as a staple in most hair care products and body lotions because it attracts moisture to the skin and the hair shaft. Chaz Dean, founder of Wen by Chaz Dean, says glycerin is one of the best-known humectants.

“I try to get people to embrace their natural curls, and glycerin aids in defining, hydrating and separating the curl.” Dean says. “I am full force on glycerin and anything that is moisturizing and hydrating to the hair because you are then able to embrace what you innately have in your texture.”

Glycerin is a sweet-tasting, colorless, thick liquid that comes from animal or vegetable fats in the soap-making process. Up until the 19th Century, glycerin was mostly produced by the candle-making industry that made candles from animal fats at that time.

In 1889, they figured out how to extract glycerin as a byproduct of soap. In case you didn’t know, soap is made from lye and fats. And it’s these animal and vegetable fats that contain anywhere from seven percent to 13 percent glycerin. Aside from skin and hair care products, you may find glycerin in cough syrup (to enhance the flavor) and even in some foods (working as a humectant and sweetener). Most beauty products use the vegetable source as the emollient.

"I included glycerin in my Luscious Curls line since it helps to hydrate the hair by attracting and retaining moisture,” says renowned stylemaker Frederic Fekkai. “It's especially great for curly hair types since it helps smooth the hair to reduce frizz and helps keep the flexibility of the curls.”

“We use it mainly for moisture retention in the product and the hair and skin,” adds John Davis, cofounder and director of AG Hair Cosmetics. “With regard to curly hair, hair is comprised of protein, and having more moisture helps to maintain curl in the hair. It helps to encourage curl.”

Despite a perception that glycerin causes hair color to fade, Coulton says it's fine to use as long as you wait a few days to use it after you color.

"If you apply it to freshly applied hair color, it can cause fading, just like using harsh shampoos or washing the hair at all within 48 hours of coloring can cause fading," Coulton say.

Because the haircolor may not "set" until a few days after coloring, glycerin may dislodge color particles by making them slippery, allowing them to "escape the shaft."

"Glycerin in itself does not bleach the hair or make it lighter," Coulton stressed. "It's gotten a bum rap because of its 'color lightening' effects, but they are no worse than any other conditioner with proteins and oils, which also are not recommended for use soon after coloring. I have colored hair and I listen to the rules that were taught to me in beauty school, and I haven't had any problems with glycerin."